1. Field of the Invention
The present invention relates to a traction type electric injection molding machine that draws a movable platen toward a fixed platen to clamp a mold. In particular, the invention relates to such a machine driven by an electric motor.
2. Detailed Description of the Prior Art
A hydraulically driven traction type injection molding machine includes a mold clamping apparatus, which includes a fixed platen and a movable platen. A pair of hydraulic cylinders are fitted on the right and left sides of the outer face of the fixed platen. The pistons of the cylinders insert through the fixed platen and protrude on both sides of the inner face of the platen. The movable platen is connected to the outer ends of the pistons and can be drawn toward the fixed platen by the hydraulic cylinders.
The mold clamping apparatus includes a hydraulic mechanism, a toggle mechanism, etc. for moving the movable platen toward and away from the fixed platen and clamping a mold. The clamping mechanism does not need to be installed on the machine bed in the rear of the movable platen and is consequently simple. When the movable platen moves relative to the fixed platen, it is possible to take out products at an end of the machine bed. A belt conveyor or another conveyor may be installed under or below the bed end. This makes it possible to collect products from a number of molding machines arranged side by side. The mold clamping positions on the molding machines are adjacent to the working passages. This facilitates mold replacement, maintenance and other work. Such structure is considered to be very advantageous particularly for small molding machines.
An electric injection molding machine can be driven by electric servo motors or other electric motors. A mold can be clamped by motion transformers that are mechanisms for transforming the rotational motion of the electric motors into linear motion each by means of a screw shaft and a nut. Therefore, unlike the hydraulic molding machine, where only the hydraulic cylinders need to be fitted, it is difficult to form a mold clamping apparatus for traction by fitting the motion transformers on both sides of the fixed platen of the electric molding machine. Besides, the fixed platen needs to be large, and the two electric motors need installation spaces. It is therefore considered to be difficult to adopt mold clamping by means of traction for the electric molding machine.
In view of the foregoing situation, it is the object of the present invention to provide a new traction type electric injection molding machine that requires only one electric motor for mold clamping and only one rotational transformer, with a mold clamping apparatus installed on the top of a bed and between the front and rear ends of the bed, and with an injection apparatus installed between them, and that does not require a particularly wide fixed platen.
The present invention for the foregoing object includes a mold clamping apparatus and an injection apparatus. The clamping apparatus includes a fixed platen and a supporting platen, which are mounted oppositely on a bed and connected by a tie bar backward and forward. The clamping apparatus also includes a pair of traction rods inserting through the fixed and supporting platens. The ends of the rods protrude from both platens. The clamping apparatus also includes a movable platen fitted to the tip ends of both traction rods in such a manner that the movable platen can move toward and away from the fixed platen. The clamping apparatus also includes a traction plate fitted to the rear ends of both traction rods. The clamping apparatus also includes a motion transformer including a screw shaft and a nut. The screw shaft is fixed to the traction plate. The nut is with a pulley supported rotatably on the inside of the supporting platen. The screw shaft and the nut are in engagement with each other. The injection apparatus is supported over the bed between the fixed and supporting platens of the clamping apparatus slidably on the tie bar inserting therethrough. The injection apparatus is a screw preplasticating injection apparatus, which includes an injection plunger mechanism and a screw plasticization apparatus. The plunger mechanism is supported on the tie bar inserting therethrough. The screw plasticization apparatus is connected to an upper part of the plunger mechanism.